The production of polyurethane foam molded parts requires the treatment of the mold, which is normally made of metal, wood or resin, with a release agent where the mold surface gets into contact with the foam-forming compounds in order to allow an easy and clean demolding of the parts after polymerization. The mold surface is therefore coated with a uniform layer of the release agent, forming a releasing film, by applying various spraying techniques known to those skilled in the art.
The presently used release agents for the demolding of the molded parts usually contain release-active substances, such as e.g. oils, waxes, silicones and/or soaps dispersed in a carrier. As a carrier, either one or more organic solvents or water can be used. They will not only act as a carrier for the release-active substances and as solvent for further additives, but also, the carrier allows adjustment to an optimum concentration of active ingredients, wetting and spreading and the formation of the release film on the mold surface, and the carriers favorably influence the surface of the polyurethane molded parts. Further, prerequisites for the carrier include cost-efficiency, processing safety, and compatibility with the environment.
The greatly increased interest in the protection of the environment and the associated stricter government regulations have led to the aim of reducing to the absolute minimum the use of volatile organic solvents. Therefore, over the past few years, increased interest has been attached to the use of water as a carrier and diluent for release agents, due to its unobjectionability with regards to health and the protection of the environment.
However, water as the carrier in release agents for polyurethane molded foam parts suffers from a number of disadvantages requiring specific adaptations (c.f. H. Wochnowski, Kunststoffe, 79, 1989, 8, pp 680-683). In connection with efforts made to develop aqueous release agents reference is made to EP-A-164 501, EP-A-188 219 and EP-A-272 629.
The disadvantages of purely aqueous release agent systems compared with release agents based on organic solvents relate to mold environment contamination, the impossibility of cleaning the mold by melting the residue and resulting increased cleaning costs and (in many cases undesired) closed and frequently fatty surfaces of the polyurethane molded parts.